"[email protected]" <[email protected]> writes:

> The only place I use retain=true is MQTTPublish's LWT (and due to current 
> implementaion its 'birth' message).

I don't think it's really an MQTT rule, but all publishes to a given
topic should use the same retain setting.  Otherwise, after a receiver
goes down/up, they can get old state.

> 3. HA comes up, sends a birth message.
> 4. MQTTPublish receives it and republishes the device discovery 
> configuration.

Very good point and this sounds like a good plan.

> Note, having the device discovery message published with retain=true would 
> also work. But, I like this better. MQTTPublish supports either. Your 
> choice.
> I believe this is necessary because HA doesn't persist the device discovery 
> configuration across an outage.

I think you are correct here, in that this is the best approach for how
HA is.

Having discovery messages with retain=true is a problem because there's
no reasonable way to have them go away.

Arguably HA should persist discovery messages across restarts, with some
timer to expire them, and there should be a rule that they are regularly
republished.  I'd suggest 7.5 days to expire and daily to publish, but
this is an HA enhancement proposal in the wrong forum.

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